package com.wc.alorithm_blue_bridge._数学知识.约数.物流选址;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

/**
 * @Author congge
 * @Date 2024/6/16 11:17
 * @description https://www.lanqiao.cn/problems/18524/learning/?contest_id=191
 */
public class Main {
    static FastReader sc = new FastReader();
    static PrintWriter out = new PrintWriter(System.out);
    static int INF = 0x3f3f3f3f;
    static int p, q;

    public static void main(String[] args) {
        int T = sc.nextInt();
        while (T-- > 0) {
            p = sc.nextInt();
            q = sc.nextInt();
            int n = q - p;
            if (n == 0) {
                out.println(0);
            } else {
                int res = INF;
                for (int i = 1; i <= n / i; i++) {
                    if (n % i == 0) {
                        int py = n / i;
                        if (py - p >= 0) res = py - p;
                        if (i - p >= 0) res = Math.min(i - p, res);
                    }
                }
                out.println(res == INF ? -1 : res);
            }
        }
        out.flush();
    }
}


class FastReader {
    StringTokenizer st;
    BufferedReader br;

    FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    String nextLine() {
        String s = "";
        try {
            s = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return s;
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    // 是否由下一个
    boolean hasNext() {
        while (st == null || !st.hasMoreTokens()) {
            try {
                String line = br.readLine();
                if (line == null)
                    return false;
                st = new StringTokenizer(line);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return true;
    }
}
